Anti-piping composition for the production of metal ingots and castings

ABSTRACT

ANTI-PIPING COMPOSITIONS COMPRISING ALUMINUM AND OXIDISING AGENT ARE IMPROVED BY THE ADDITION OF A FLAME GENERATING MATERIAL SUCH AS PAPER PULP, SAWDUST, WOOD FLOUR OR COB FLOUR.

United States Patent Ofifice U.S. Cl. 75-94 8 Claims ABSTRACT OF THEDISCLOSURE Anti-piping compositions comprising aluminium and oxidisingagent are improved by the addition of a flame generating material suchas paper pulp, sawdust, Wood flour or cob flour.

This invention relates to the production of metal ingots and castings.

This application is a continuation of my parent application, Ser. No.783,703, filed Dec. 13, 1968, now abandoned.

In the production of metal ingots and castings by pouring molten metalinto a mould, the shrinkage of the metal in the body of the mould as itcools and solidifies requires that molten metal should feed from feederheads, risers, hot tops, or the head of an ingot mould, to compensatefor such shrinkage. If this is allowed to take place undisturbed, thereis formed a substantial central cavity in the head metal, a phenomenonknown as pipe.

To avoid or minimise this, it is well known practice to apply to thesurface of the metal in the mould a socalled anti-piping compound. Thisis usually a composition of which the ingredients ignite and reactexothermical- 1y when fired by the heat of the molten metal. The heatthus generated delays the solidification of the head metal and thusreduces or eliminates the formation of pipe.

The exothermic compositions used as anti-piping compounds are generallyof an aluminothermic composition i.e. containing finely dividedaluminium and oxidising agent therefore. It is possible to use aluminiumin relatively pure elemental form, as powders, turnings, sawings or thelike but since it is desirable to keep the cost of the antipipingcompound as low as possible it is convenient to use the commercialmaterial known as ball mill dust. This is the ground product from slagsobtained in the metallurgy of aluminium and usually contains alumina,flux residues and the like and aproportion of aluminium metal. Theproportion of aluminium may vary Widely depending on the source of theball mill dust but is generally 10 to 30% by weight.

The compositions contain oxidising agents for the aluminium, suitablematerials being strong oxidising agents such as alkali metal, andalkaline earth metal nitrates and chlorates, and reducible oxides suchas iron oxide and manganese dioxide.

It is also known practice to include a proportion of a fluoride, e.g. analkali metal or alkaline earth metal fluoride, or aluminium fluoride, ora mixed fluoride salt, e.g. cryolite, or a fluoro complex salt such as atitano, boro or silico fluoride.

When such exothermic compositions are ignited, they 3,728,102 PatentedApr. 17, 1973 tend to generate fumes which are noxious under foundryconditions and this is especially the case where ball mill dust is usedas the source, or part of the source, of the aluminium in thecomposition. An additional disadvantage of the generation of such fumesis the obscuring by clouds of smoke of the metal surface, so that theteeming is made more difiicult.

It is an object of the present invention to provide antipipingcompositions of the type generally set forth above, which furthercontain an additive which reduces their tendency to the generation offume.

As a result of considerable research and experiment it has been foundthat the fume emitted from such compositions on burning is itselfcapable of being ignited (and therefore rendered innocuous) but thisignition does not normally take place spontaneously.

According to the present invention there is provided an anti-pipingcomposition in powder or granular form, which comprises aluminium andoxidising agent therefor together with an organic additive which at thetemperature of the molten metal generates flame. In this way, the smokeor fumes produced on application of the composition to the molten metalare consumed in the flame by a socalled after-burner effect.

More specifically according to the invention it has been found thatorganic materials comprising high proportions of carbon hydrogen andoxygen are very suitable for the purpose and many cellulosic materialsare of value, for example, paper pulp, wood pulp and shredded paper.Materials such as wood flour and the like are particularly suitable. Thematerial should preferably have a low bulk densitypreferably 0.2-0.4gm./cc.-and a low moisture content. Examples of such materials are woodflour and sawdust (preferably from hard wood and of particle sizepassing a 10 B88 mesh but without a substantial quantity passing a E88mesh), ground cobs or cob flour, grain hulls and nut shells, withpolystyrene and similar plastics chips, cereal flours, and organic gumssuch as sulphite lye and gum arabic being usable but not preferred. Aparticularly preferred materials is 20+ 100 E58 mesh cob flour.

The optimum quantity of such additive to the anti-piping composition forthe purpose specified will vary with the particular anti-pipingcomposition but will generally be 1- 2.0%, preferably 5-15% by weight.Particularly good results have been obtained by the use of the additivesin quantity of the order of 10% by weight.

The improved compositions of the present invention may contain aluminiumin any of the forms indicated above and any of the oxidising agents, orfluoride additions mentioned above. They are used in conventional mannerby sprinkling the powdered or granular composition onto the surface ofthe molten metal.

It is further of value to include in the anti-piping composition of thisinvention a proportion of a humectant such as glycol or glycerol, in aproportion of 1-20%, preferably 5-15% by weight of the composition toaid in reducing dust from the material. Such materials have theadditional advantage of supplying plenty of hydrogen and oxygen forburning, while not supplying much carbon, and they thus aid in reducingthe smoke and fume from the anti-piping agent.

Further, the anti-piping compositions according to this invention maycontain a flame retardant which serves to spread the action of theanti-piping compound over a period of time rather than allowing it toproceed violently for only a short period of time. Suitable materialsfor this purpose are silica flour and sodium chloride.

3 The following examples of anti-piping compositions according to theinvention will serve to illustrate the invention:

EXAMPLE 1 The following anti-piping compositions are formulated (inpercentages by weight):

Aluminium foil 4 Washed ball mill dust 52 Alumina 15 Calcined magnesia(minus 150 BSS mesh) 13 Sodium nitrate 9 Haematite 4 Sodium aluminiumfluoride 2 Sodium fluoride l Washed ball mill dust (18% aluminium) 83Sodium nitrate 7 Millscale Sodium aluminium fluoride 3 Sodium silicofluoride 2 To each of the foregoing compositions there was added variousproportions of: cob flour, hard-wood flour, plastics chips, groundnut-shells, grain hulls, and the resulting mixtures were tested toobserve the extent to which they generated visible fumes. It was foundthat in each case a proportion of of the wood flour additive, by weightof the composition A or B, was the most suitable. In each case, a markedreduction in fume evolution was observed; the amount of fume generatedwas visually estimated as about 10% of that generated using anti-pipingcompounds in which the flame generating additives had not been included.

EXAMPLE 2 An anti-piping composition was made up as follows (proportionsby weight):

To samples of this composition was added 10% cob flour of -16+100 BSSmesh and to other samples 10% of cob flour of 20+60 BSS mesh. Suchsamples, together with control samples, were tested by placing aquantity of material on a flat surface at 1400" C. The flour containingsamples each burnt for about 4-5 minutes with vigorous flaming butlittle visible fume. The control samples generated about 510 times morevisible fume than the flour containing samples.

It was found that easier mixing was achieved With the -20+60 mesh flour.If too fine an additive is used, the composition tends to burnundesirably fast; if too coarse, homogeneous mixtures are difficult toobtain. It was also found that the incorporation of the flame generatingingredient did not adversely affect the exothermic properties of theanti-piping compositions.

I claim as my invention:

1. In a granular anti-piping composition for application to the surfaceof molten metal during casting thereof, the composition consistingessentially of aluminum and an oxidizing agent therefor and wherein thecomposition generates fumes upon its ignition after application to thesurface of the molten metal, the improvement comprising including in thecomposition 1 -20% by weight of an organic additive, said organicadditive being capable of generating a flame at the temperature of themolten metal and being present in an amount sufficient to consume thefumes produced by the composition.

2. An anti-piping composition according to claim 1 wherein the organicadditive is cellulosic fibrous material.

3. An anti-piping composition according to claim 1 which includes ahumectant in an amount of 1-20 by weight of the composition.

4. An anti-piping composition according to claim 1 which contains aproportion of a flame retardant.

5. In a method of casting molten metal comprising pouring said metalinto a mold and applying to the surface of said molten metal duringsolidification in the mold a granular exothermic anti-piping compositioncontaining aluminum and an oxidizing agent therefor, whereby applicationof the composition to the molten metal generates fumes, the improvementcomprising applying to the surface of said molten metal with saidanti-piping composition an organic additive which generates a flame atthe temperature of said molten metal the additive being applied in anamount sufiicient to substantially consume the generated fumes.

6. An anti-piping composition according to claim 1 wherein the organicadditive is a member selected from the group consisting of paper pulp,shredded paper, wood flour, sawdust and cob flour.

7. A method according to claim 5 wherein the organic additive is acellulosic fibrous material.

8. A method according to claim 5 wherein the organic additive is amember selected from the group consisting of paper pulp, shredded paper,wood flour, sawdust and cob flour.

References Cited UNITED STATES PATENTS 1,533,892 4/1925 Osborne 164- 422,937,425 5/1960 Morgan 27 X 3,123,878 3/1964 Davidson 10638.2 X

FOREIGN PATENTS 969,331 9/ 1964 Great Britain 75--94 1,094,233 12/ 1967Great Britain 7594 798,710 7/1958 Great Britain l64--53 921,332 3/1963Great Britain 7594 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU,Assistant Examiner US. Cl. X.R.

